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Night-rate tariffs: charging when power is cheapest

Many power plans in New Zealand and Australia price electricity differently by time of day. Overnight, when demand is low, power is often cheaper.

How time-of-use pricing works

In general terms, time-of-use plans split the day into periods such as peak, shoulder and off-peak, each with its own price per kilowatt hour. Night rates usually cover the late evening to early morning, when demand is lowest. Some older setups run a separate controlled night circuit for things like hot water. The details vary a lot between retailers, networks and states, so the only reliable source is your own plan and bill.

What it would keep running

  • Overnight electrolyser runs
  • Battery top-up in off-peak hours
  • Controlled hot water on the night circuit
  • Dishwasher and washing machine timed for night
  • Storage kept full between outages

What it means for hydrogen

The system is designed to charge on off-peak grid power, running the electrolyser overnight to fill the hydrogen buffer and top up the battery. Because round-trip efficiency is 30% or less, each stored kilowatt hour costs several night-rate kilowatt hours. So cheap night power reduces the cost of keeping storage full, but it does not make stored energy cheap.

If your night rate is not much lower than your day rate, hydrogen storage is purely about backup, not money. Even with a big gap between the two, treat any savings as uncertain until your actual plan, daily charges and usage have been run through the numbers for your house.

How it works →
The H2OME loop: an electrolyser splits water into hydrogen, the hydrogen is stored in a tank for weeks, a fuel cell turns it into electricity for your home, and the water returns to the loop.

Questions to ask your retailer

Before relying on night-rate charging, ask which hours count as off-peak, whether you need a smart meter, whether the off-peak price applies to the whole house or only a controlled circuit, and whether there are higher daily charges on time-of-use plans. Ask too whether plans change if you add a large new load. Write the answers down, because they will be needed to size charging properly.

Questions

Will night-rate charging save me money?

Not necessarily. It reduces the cost of filling storage, but with round-trip efficiency of 30% or less, stored power costs more than the night power used to make it. Treat the system as backup and resilience, not a saving.

Do I need a smart meter?

Most time-of-use plans need a meter that records when you use power. Many homes already have one. Your retailer can tell you whether your meter supports the plan you want.

Can the system charge only during off-peak hours?

Yes, it is designed to charge on off-peak power. Charging windows would be set to match your plan's hours so the electrolyser runs when power is cheapest. If your retailer changes those hours, the windows need updating to match.

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